This invention relates to a focusing controlling device which is used in a camera or the like, to change the amount of extension of the photographing lens according to the position of the object.
A variety of automatic focusing devices have been proposed in the art. One of the automatic focusing devices is an active system. In this system, light is applied from the camera to the object, and light reflected from the object is received to measure the distance between the camera and the object. In a system of this type, a range finding operation is generally carried out according to the principle of triangulation. In the range finding operation, a light beam reflected from the object is applied to a light receiving element which is faced in the same direction as the photographing lens, and the photographable range is scanned with an infrared beam, so that the distance is measured from the angle of the optical axis of the infrared beam applied to the light receiving element. In another example of a conventional automatic focusing device, a number of light receiving elements are arranged in a line, a light beam is applied in the direction of the optical axis of the photographing lens, and the distance is measured by finding the order of the light receiving element to which the light beam is incident. However, the former device suffers from a problem that it is low in durability because it employs the scanning beam operation; while the latter device is disadvantageous in that it is expensive because it uses a number of light receiving elements which are considerably small in size.